The Evolution of Groundwater Hydrochemical Characteristics Under Coal Mining Conditions—A Case Study in Western China

To evaluate the dynamic evolution of the groundwater chemical characteristics in multi-layer aquifers under coal mining conditions, this study takes Qinglong Coal Mine as a typical case for systematic analysis. A comprehensive research method combining hydrochemical analysis and numerical simulation is adopted, coupling MODFLOW, MT3D, and PHREEQC modules to simulate the synergistic changes in the groundwater flow field and hydrogeochemical reaction during coal mining. The results show that among the studied aquifers, the coal seam aquifer (P3l) has the worst water quality and is most obviously disturbed by mining activities, with its hydrochemical genesis mainly controlled by water–rock interaction. After mining, groundwater depression cones are formed near pumping wells. Fissure development-induced leakage recharge enhances hydraulic connectivity between aquifers. The P3l aquifer undergoes slight acidification with a significant increase in SO42− concentration, while the overlying roof aquifers (P3c and T1y) show gentle hydrochemical changes, with ion concentration anomalies mainly occurring at fissure penetration zones. Overall, coal mining not only alters the groundwater flow field but also transforms the underground environment from a reducing to an oxidizing state. Thereby, it significantly affects the groundwater chemical composition in the mining area. This study provides a scientific basis for groundwater environment protection and rational development of groundwater resources in coal mining areas.